Residential and commercial buildings represent a prime opportunity to improve energy efficiency and sustainability in the United States. The buildings sector alone accounts for 40% of the United States' yearly energy consumption (40 quadrillion BTUs, or “quads”, out of 100 total), and 8% of the world's energy use. Lighting and thermal management each represent about 30% of the energy used within a typical building, which corresponds to around twelve quads each of yearly energy consumption in the US. Windows cover an estimated area of about 2,500 square km in the US and are a critical component of building energy efficiency as they strongly affect the amount of natural light and solar gain that enters a building. Recent progress has been made toward improving window energy efficiency through the use of inexpensive static coatings that either retain heat in cold climates (low emissive films) or reject solar heat gain in warm climates (near-infrared rejection films).
Currently, static window coatings can be manufactured at relatively low cost. However, these window coatings are static and not well suited for locations with varying climates. An electrochromic (EC) window coating overcomes these limitations by enhancing the window performance in all climates. EC window coatings undergo a reversible change in optical properties when driven by an applied potential. Some EC devices may include a working electrode, a solid state electrolyte, and a counter electrode sandwiched between two transparent conductor layers and an outer glass layer. The working electrode may include nanocrystalline structures or amorphous metal oxide nanoparticles such as WO3, CSxWO3, NbOx, TiO2, MoO3, NiO2, and V2O5.
As part of the EC device fabrication process, the working electrode, solid state electrolyte, and counter electrode may be exposed to high temperatures as part of a tempering or heat quench process. For example, the EC device layers may be exposed to temperatures of 650° C. or higher. At these temperatures, some of the layers of the EC device, and in particular the working electrode, may undergo sintering or other undesirable crystallization changes or phase transitions. These changes may affect the operation or efficiency of the EC device.